1. Field of the Invention
The present invention relates, in general, to a radiation source assembly used in a nondestructive inspection process and a connector press used in producing such assemblies and, more particularly, to an Ir-192 radiation source assembly, with a source capsule having double-sealed radiation source discs and two connectors, or a cap connector and a female connector being respectively coupled to both ends of a pigtail, and to a connector press used for compression-connecting the two connectors to both ends of such a pigtail so as to form a desired radiation source assembly.
2. Description of the Prior Art
In order to produce a radiation source used in a nondestructive inspection, a plurality of Ir-radiation source discs have been conventionally used. Some countries import radiation source disc targets from foreign countries. Such disc targets are primarily processed products, and so they must be pre-processed and finally processed before they are exposed to neutrons within a nuclear reactor. A conventional pre-process and a conventional final process for the disc targets will be described as follows.
Primarily, both diameter and thickness of such a disc target are measured prior to inspecting any external defect of the disc target with the naked eye. Sometimes, such a naked eye inspection may discover a defect on one surface of a disc target.
Thereafter, the flatness of the disc target is measured. Since conventional radiation source disc targets are typically produced through a punching process, the disc targets fail to have a desired flatness. Therefore, it is necessary to flatten the radiation source disc target with a nonmetal hammer while interposing the disc target between two flat metal discs. When the radiation source disc target fails to accomplish a desired flatness, it is almost impossible for the disc target to perform a desired operational performance of a point source or to provide a high quality nondestructive inspection image.
It is also necessary to completely remove micro debris from the surface of the radiation source disc target since such micro debris may cause a radioactive contamination.
After the pre-process, the radiation source disc target is washed using neutral detergent and distilled water, and is finally ultrasonically washed prior to being dried, thus completely preparing a desired radiation source disc target. The dimension of the disc target is measured and is compared with calculated values. The prepared disc target is an Ir-metal type disc having a diameter of 2.5 mm, a thickness of 0.25 mm, a weight of 27.6 mg/disc, a nuclidic purity of 99.9%, and a specific weight of 22.5 g/cm3.
After preparing the radiation source disc targets and manufacturing a radiation source capsule, a desired radiation source is produced. In order to produce a desired radiation source, a plurality of disc targets, enclosed within an aluminum irradiation container, are exposed to neutrons within a neutron irradiation hole of a multi-purpose nuclear reactor for a predetermined period of time. After the neutron irradiation process, the irradiation container is removed from the neutron irradiation hole of the nuclear reactor and is received within a carrier vessel, and is moved to a concrete hot cell along with the vessel. Within the concrete hot cell, the irradiation container is removed from the carrier vessel by a manipulator. The irradiation container is, thereafter, set in automatic classifying and measuring equipment. When a control unit of the equipment is turned on, the container is automatically processed through a container cutting process, a radioactivity measuring process, and a classified radiation source capsuling process in accordance with a program of the control unit. In such a case, the Ir-disc targets from the radioactivity measuring process are received within a stainless capsule in a way such that 5 to 10 disc targets are received within each capsule. The stainless capsule is, thereafter, closed by a lid prior to being welded into a single structure at the junction between the capsule and the lid through a plasma arc welding process, thus forming a sealed radiation source.
When such a radiation source capsule is completely produced, a desired radiation source assembly is produced. An example of conventional radiation source assemblies is shown in the accompanying drawing, FIG. 1.
As shown in the drawing, the radiation source assembly 1 comprises a source capsule 3, a female connector 5 and a pigtail 7. In such a case, the source capsule 3 is made of SUS 316L, and consists of a cap connector 9, an outside cap 11 and an inside capsule 13. As best seen in FIG. 2, the cap connector 9 receives one end of the pigtail 7, while the outside cap 11 is welded to the cap connector 9 through a TIG welding process. The inside capsule 13 is set within the outside cap 11.
In order to receive the inside capsule 13, the outside cap 11 has a cavity. The above cap 11 also has an arcuate cross-section, with the tip of the cap 11 being rounded. The object of such a rounded tip of the cap 11 is to minimize a kinetic resistance generated at the tip when the radiation source assembly passes through guide tube of a nondestructive inspection apparatus. The inside cap 11 is fitted over a connecting projection 31 of the cap connector 9 at its fitting opening prior to being integrated with the connector 9 into a single structure through a TIG welding process.
The cap connector 9, connected to the pigtail 7, is a cylindrical member provided with a pigtail fitting hole 15. The connecting projection 31 is provided on an end of the cap connector 9 opposite to the pigtail fitting hole 15.
As shown in FIG. 3, the inside capsule 13, set within the outside cap 11, consists of a cylindrical outside case 14, a sealing cover 16 and a filler 17. The outside case 14 receives a plurality of radiation source disc targets 10 in a way such that the targets 10 are regularly stacked. The sealing cover 16 is fitted into the top open end of the outside case 14, thus sealing the outside case 14. The filler 17 is interposed between the sealing cover 16 and the stacked targets 10 so as to press the targets 10.
As best seen in FIGS. 4a and 4b, the pigtail 7 consists of a wire core 23, a primary coil 25, a secondary coil 27, and a large-diameter coil 29. The wire core 23 is made by twisting a plurality of wires 21, the primary coil 25 is wound around the wire core 23. The secondary coil 27 is wound around the primary coil 25. The large-diameter coil 29, having a predetermined regular pitch, is wound around the primary coil 25 along with the secondary coil 27. In such a case, all the wires and coils of the pigtail 7 are made of carbon steel, and so they have a predetermined elasticity. The wires and coils of the pigtail 7 are not undesirably wear-cut or loosened even though the pigtail 7 is used ten thousand or more times. The wires and coils are also free from corrosion even when they are exposed to atmospheric air.
The above radiation source assembly 1 passes through a guide tube under the control of a manipulation handle connected to a male connector engaging with the female connector 5 of the assembly 1. The assembly 1 is thus finally received within a radiation source carrier. Such an assembly 1 enclosed by the radiation source carrier is used with a nondestructive inspection apparatus. During a nondestructive inspecting operation, the assembly 1 reaches an inspection point by the guide tube. When the radiation source assembly 1 is kept within the radiation source carrier, a stop ball 19, formed on one end of the female connector 5 positioned at the rear end of the assembly 1 as shown in FIG. 5, is locked to an inside wall of the carrier, thus being firmly and precisely positioned within the carrier. This finally completely prevents a radiation leakage, caused by an assembly 1 failing to be precisely positioned within the carrier.
In the conventional radiation source assembly 1, the source capsule 3 and the female connector 5 are locked to both ends of the pigtail 7 through a compressing process. That is, as shown in FIGS. 2 and 5, both ends of the pigtail 7 are primarily fitted into the first pigtail fitting hole 15 of the cap connector 9 of the source capsule 3 and the second pigtail fitting hole 18 of the female connector 5, respectively. Thereafter, the female connector 5 and the cap connector 9 are inwardly compressed in a radial direction using a dedicated connector press until the two connectors 5 and 9 are locked to both ends of the pigtail 7. However, the conventional radiation source assembly 1 is problematic in that the two connectors 5 and 9 may be unexpectedly removed from both ends of the pigtail 7 during an operation of the assembly 1.
In addition, when the two connectors 5 and 9 are fitted over both ends of the pigtail 7, the ends of the pigtail 7 may fail to completely reach the inside ends of the fitting holes 15 and 18 of the two connectors 9 and 5 in accordance with the linearity of the pigtail 7, the flatness and linearity of the fitting holes 15 and 18 of the two connectors 9 and 5, and/or the pressure applied to the source capsule 3 and the female connector 5 while fitting the capsule 3 and female connector 5 over both ends of the pigtail 7. It is thus almost impossible to assure desired positions of both ends of the pigtail 7 within the two connectors 5 and 9 prior to compressing the two connectors 5 and 9 over the pigtail 7. Furthermore, the inserted lengths of the pigtail 7 within the two connectors 5 and 9 are not sufficient to provide a desired linearity of the assembly 1 after the connectors 5 and 9 are compression-locked to both ends of the pigtail 7.
In the above radiation source assembly 1, the outside case 14 of the inside capsule 13 is closed by and welded to a sealing cover 16 while accomplishing a desired sealing effect, with the disc targets 10 and the filler 17 being set within the outside case 14. When the number and/or thickness of the stacked disc targets 10 does not agree with the length of the filler 17, the disc targets 10 may slip on each other or may be separated from each other within the outside case 14. In such a case, the disc targets 10, or the point sources of a radiography, may be movable during a nondestructive inspecting operation of the assembly 1, thus failing to provide a clear image and to provide precise nondestructive inspecting results.
On the other hand, the cap connector 9 of the source capsule 3 is welded to the pigtail 7 through a TIG welding process. However, the materials of both the capsule 3 and the pigtail 7 may be undesirably changed in their physical characteristics due to heat generated during the TIG welding process, thus causing a thermal defect and a thermal deterioration at the welded junction between the cap connector 9 and the pigtail 7. In an effort to overcome such a thermal defect and such a thermal deterioration at the welded junction between the cap connector 9 and the pigtail 7, the cap connector 9 may be locked to the pigtail 7 through a compression process rather than the welding process.
As shown in FIG. 6, such a compression process of locking the cap connector 9 to the pigtail 7 uses a dedicated connector press 51. The conventional connector press 51 compresses the cap connector 9 of the source capsule 3 with the pigtail 7 being fitted into the cap connector 9, thus locking the capsule 3 to the pigtail 7 and making a desired radiation source assembly. In such a case, the target portion to be compressed is the overlapped portion of the cap connector 9 engaging with the pigtail 7.
When the cap connector 9 of the capsule 3 is compression-locked to the pigtail 7 using the press 51 consisting of top and bottom dies 53 and 55 as shown in FIG. 6, there is a deviation of the compression force in an axial direction of the pigtail 7, with the compression force being applied to the overlapped portion of the cap connector 9 engaging with the pigtail 7, even though the compression force is uniformly distributed on the overlapped portion in a vertical direction. Therefore, it is almost impossible for a resulting assembly 1 to have a desired linearity.
The radiation source assembly 1 failing to have such a desired linearity does not accomplish required conditions of assemblies. Such an assembly 1 may be also excessively abraded when it repeatedly moves within the guide tube in opposite directions, and so the assembly 1, having a dangerous radioactive material, may fail to accomplish a desired degree of operational safety and may cause a radioactive contamination.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a radiation source assembly, of which each of the cap connector and the female connector is provided with internal round threads on its pigtail fitting hole, thus engaging with the large-diameter coil of the pigtail at the internal round threads through a thread engagement prior to a compression process and being almost completely prevented from an unexpected removal from the pigtail, which allows a person to know whether both ends of the pigtail fully reach desired points within the two connectors, thus securing a precise compressing target portion, and of which the inserted lengths of the pigtail relative to the two connectors are maximized, thus accomplishing a desired linearity of the assembly.
Another object of the present invention is to provide a radiation source assembly, which is provided with a target biasing spring on the capsule lid for allowing the disc targets within the source capsule to effectively maintain a desired condition as point sources regardless of the number of targets, with a capsule lid biasing device being provided on a dedicated welding jig for allowing the capsule lid to be welded to a capsule body while maintaining the disc targets in the states of point sources and improving the weldability of an inside capsule of the source capsule.
A further object of the present invention is to provide a connector press used in producing the radiation source assemblies, which accomplishes a desired compression locking of the source capsule to the elastic pigtail by simultaneously compressing the capsule at regularly and angularly spaced points through a multi-point compressing process, and which thus accomplishes a desired linearity of the capsule and the pigtail, and prevents the capsule from causing an operational error or being abrasion-damaged due to a frictional resistance generated at the capsule when the capsule repeatedly moves within a guide tube in opposite directions.
The above-mentioned primary object of this invention is accomplished by a radiation source assembly, comprising a source capsule enclosing a radiation source, a female connector connected to a male connector coupled to a manipulation handle, and a pigtail connecting the source capsule and the female connector together, wherein a cap connector of the source capsule has first internal threads on its pigtail fitting hole, with the first internal threads having a profile corresponding to a large-diameter coil of the pigtail and engaging with the large-diameter coil of a first end of the pigtail through a thread engagement.
In the above assembly, the female connector has second internal threads on its pigtail fitting hole, with the second internal threads having a profile corresponding to the large-diameter coil of the pigtail and engaging with the large-diameter coil of a second end of the pigtail through a thread engagement. The number of each of the first and second internal threads is four or more.
The above-mentioned second object of the present invention is accomplished by a radiation source assembly, comprising: a capsule body receiving stacked radiation source disc targets; a capsule lid fitted into an open end of the capsule body and welded to the capsule body, thus sealing the capsule body; and a coil spring set within a spring seat hole of the capsule lid and adapted to normally bias the radiation source disc targets within the capsule body in a direction after the capsule lid is welded to the capsule body.
The above-mentioned third object of the present invention is accomplished by a connector press for producing a radiation source assembly by compression-locking a source capsule to a first end of a pigtail of the assembly, with the source capsule being fitted over the first end of the pigtail prior to a compression-locking process of the press, comprising: a plurality of compression punches radially arranged on a holding disc at regularly and angularly spaced positions to compress an overlapped portion of the source capsule fitted over the pigtail at regularly and angularly spaced external points; a plurality of pressure rods hinged to an edge of a support at regularly and angularly spaced positions and adapted to respectively and inwardly push the compression punches in a radial direction of the holding disc at outside ends of the punches; and a reciprocable push rod being movable in opposite directions in cooperation with a cylinder actuator so as to synchronously rotate the pressure rods around hinge points of the pressure rods, thus allowing the pressure rods to be opened or closed at their punch pushing ends and to selectively push the compression punches inwardly in the radial direction of the holding disc.
In the above connector press, each of the compression punches is movably received within a radial guide member of the holding disc, thus being radially reciprocable on the holding disc under the guide of the guide member, with a compression tip having a radius of curvature equal to a desired compressed radius of the source capsule and being removably attached to an inside end of each compression punch, and a return spring connecting each of the compression punches to the holding disc so as to elastically return each compression punch to its original position within the guide member when an external force is removed from each compression punch.
In addition, each of the pressure rods is provided with a roller at an end opposite to its punch pushing end. On the other hand, the push rod is provided with a truncated conical push block at an outside end thereof, the push block having an inclined surface due to its truncated conical shape, with rollers of the pressure rods being brought into rotatable contact with the inclined surface of the push block, thus allowing the pressure rods to be synchronously closed at their punch pushing ends when the push rod is moved toward the support of the pressure rods by a driving force of the cylinder actuator.
The above connector press further comprises: a scale rod movably inserted at a center of the support and adapted for supporting a tip of the source capsule; and an adjusting screw radially and movably threaded into the support from the outside to the center of the support and adapted for holding or releasing the scale rod within the center of the support.